!!99!!General help
This program provides astro navigation
for ocean navigation. The built in 
almanac is computed for each sight and
will operate between the years 1970
and 2099. With an accuracy generally
better than .1 of a nautical mile.

!1REMEMBER
Do not rely on any electrical form of 
navigation for passage making. Use this
program to check manual calculations or
for providing additional fixes.
!1H.Edwards excepts no
!1responsibility for losses or 
!1damage caused by use of this
!1program.
!!01!!Astro Menu
The options are grouped into three
sub menus:
- Almanac (general body information)
- Sight entry and position fix
- Setup
!!02!!Update Defaults
These defaults are used on many of
the entry screens and should be set
to suitable values.
!2Index error
  The uncorrected error in the sextant.
  This is entered in seconds of arc.
  The error can either be ON the arc
  and thus all uncorrected measurements
  taken with the sextant will be larger
  by this amount. Or OFF the arc.
!2Height of eye
  above sea level is entered in meters.
!!04!!Save Defaults
The defaults can optionally be saved
to disk for use next time the 
program runs, or not saved and used
only for this session
!!05!!Compute Hc & Az
This option computes the height and
azimuth of the specified body.
Specify date,time,latitude and longitude
for the observation.
Latitude & longitude may be entered as
degrees and decimal minutes or as 
signed decimal degrees.
!1eg. 49 34.4S or -49.5733
!!06!!Display Hc & Az
!2Brightness (ONLY STARS)
Shows the absolute magnitude, the
smaller the value the brighter.
!2RA  - Right Ascension
Angular distance Eastward from First
Point of Aries to point where a Great
Circle through the Pole and the body
cuts the Equator. Displayed in hours
minutes & seconds.
!2GHA - Greenwich Hour Angle
Angle between the Greenwich Meridian
and a Meridian through the body.
Displayed as degrees, minutes and
decimals measured Westward from
Greenwich.
!2LHA - Local Hour Angle
Angle between Longitude of observers
position and Longitude of the Meridian
of the body. Displayed as degrees,
minutes and decimals measured Westward
from observers Longitude.
!2DEC - Declination
Angular distance of a body (N)orth or
(S)outh of Celestial Equator.
!2Hc  - Calculated Height
Angular distance from the horizon to
the body at the observers position and
height of eye.
NOT VISIBLE is displayed when the
calculated height is less than 0
degrees.
!2Az  - Azimuth
True bearing of the body at the
observers position.
!!07!!Fix sight
Enter the estimated position EP at the
time the fix is required. For a running
fix this needs to allow for distance
run, tidal set and leeway. For a
straight fix where two or more bodies are
sighted together enter the same EP as
used in the sight entry. 
This EP may be a position many miles
from the final fixed position.
!!08!!Fix sight
The fixed position is displayed as
latitude and longitude.
!!09!!Sight Entry
Enter the date and time of the fix in
GMT, this needs to be accurate to the
second. Enter the sextant altitude of
the sight Hs and the estimated position
EP. For a running fix the EP needs to be
as accurate as possible. For a fix where
the observers position does not change
between sights, then any EP can be
used, provided it is set the same for
each entry.
!1REMEMBER
Set index error and height of eye using
defaults entry prior to entering sight.
!!10!!Sight Entry Result
Check the sextant height Hs, Index Error
IE and Height of Eye.
!2H
The Apparent Altitude is the sextant
altitude corrected for Index error and
Dip (Height of Eye)
!2Refraction
Correction for the bending of light as
it passes through the Earth's
atmosphere.
!2Semi-diameter
Angular correction for viewing top or
bottom limb of body as opposed to
centre.
This is only used for the Sun and Moon.
All other bodies should be sighted for
centre.
!2Parallax
Angular correction allowed for viewing
a body from two different positions.
!2Ho
The Observed Altitude is the Apparent
Altitude corrected for Refraction,
Semi-diameter and Parallax. This is the
actual altitude from celestial horizon.
!!11!!Sight Entry Result
!2Ho - Observed Altitude
is the Apparent Altitude corrected for
Refraction, Semi-diameter and Parallax.
This is the actual altitude from
celestial horizon.
!2Hc - Calculated Height
Angular distance from the horizon to
the body at the observers position and
height of eye.
!2Az - Azimuth
True bearing of the body at the
observers position.
!2p - Intercept
Is the difference between the Observed
altitude and the calculated altitude
(Ho-Hc).
!!12!!Clear Sights
This will clear the sights which have
been entered without exiting the
program. Use this before entering a new
fix.
!!13!!Choose Sight
Choose an existing sight to change any
values or pick NEW SIGHT to enter a new
sight. Up to 5 sights can be used to
calculate a fix.
!!14!!Rising & Setting
This option calculates the times for
rising,setting and transit for any 
given body at an observed position.
Enter the required date and position
as latitude and longitude. 
Latitude & longitude may be entered as
degrees and decimal minutes or as 
signed decimal degrees.
!1eg. 49 34.4S or -49.5733
!1Ensure
an appropriate height of eye is set as
default.
!!15!!Rising & Setting Results
The time of body rising, setting and
transit is shown. The rising and
setting times are when the body is on
the observers horizon. For the sun Civil
(6 degrees below), Nautical (12 degrees
below) and Astronomical (18 degrees
below) are given. Civil twilight is the
best time for star sights.
On some days certain stars have two
transits, this will show as two times.
The time of rising will be computed on
the chosen day. However the transit
and setting times are always computed
to be after the rising time, which some
times means the time stated will be on
the following day.
!2AA:AA
is shown if the body remains above the
limit for the 24 hour period.
!2BB:BB
is shown if the body remains below the
limit for the 24 hour period.
!!16!!Choose body
Enter the name of the body to be
observed. If you are unsure of a
spelling enter a partial name to be
prompted with all matches. On a registered
program all navigational planets, stars,
sun and moon are supported.
Aries can also be entered as a body.
!!17!!Identify body
This option is used to identify which
bodies occupy a selected area of the
sky. Enter the date,time and position
of the observation.
!!18!!Identify body
Enter the altitude of interest.
The range in altitude over which the
display will be based. eg. 5 will show
any bodies at + or - 5 degrees of the
altitude.
The true bearing to the body and the
range of the bearing.
!1EG.
  altitude 0,range 90,bearing 0,range
  180 to show all bodies above the
  horizon.
Keep both ranges small if you wish
to identify a particular body.
!!19!!Identify display
The calculated height Hc and azimuth Az
are only calculated approximately to
an accuracy of one degree.
Brightness of stars is shown, the 
smaller the value the brighter.
!!20!!Plot fix
The fix can plotted on the screen to
show the accuracy of the sights. This
option is only available with three or
more sights.
!!21!!Plotted fix
The fix is shown at the centre 
co-ordinate 0,0 around this is drawn
an ellipse. This shows the limit within
which there is a 95% probability the
position lies. The scale is in
nautical miles. Press a digit key
corresponding to the number of the
sight to see a plot of the sight. 
Pressing it again will clear the plot.
Press 'A' to plot all. Esc to exit.
!!22!!Enable/disable Sight
Sights can be disabled from being used
when computing a fix. This enables
suspect sights to be excluded.
Initially all sights are used. Enter
the number of the sight to
disable/enable.
!!23!!Save sight
Sight information can be saved to a 
named file for latter retrieval.
The default directory is \NAVDATA\
with an extension .SGT
!!24!!Load sight
Sight information can be retrieved
from previously stored data.